When I was nine, I read a comic strip version of Sir Arthur Conan Doyle's South American adventure novel, The Lost World. Captivated by images of cloud-reaching, flat-top, cliff-sided mountains gushing with waterfalls and wildlife, I dreamed of visiting the mysterious, remote region of Venezuela on which the book was based.

Forty years later, that childhood dream has just been fulfilled. My great adventure began with a flight from the Venezuelan capital, Caracas, to the provincial city of Ciudad Bolivar. From there, I headed for the real lost world - a distant region called La Gran Sabana, situated in the south-east corner of the country, near the borders with Brazil and Guyana.

At 9am on a sunny Saturday morning, I kissed civilisation goodbye and boarded a 40-year-old, six-seat, single-engine Cessna for the 500km flight from Ciudad Bolivar to Gran Sabana's only town, Santa Elena de Uairen. This almost toy-like plane made a racket like a lawn mower. The seat in front was piled high with frozen chickens for delivery to far-flung villages. They had a seat belt. I didn't. There were no parachutes either. The doors and windows closed with simple pull-to handles. No locks. Deluded or not, I felt a weird combination of nervous exhilaration and serene security.

Because our plane had no navigational aids, it was visual flying all the way. We zigzagged from one landmark to another, dipping under clouds to keep track of where we were going. Below was a wild, uninhabited landscape of virgin jungle, meandering rivers and awesome waterfalls. Above our low-flying plane soared towering tepuis. These sheer-sided, table-top mountains - some over 2,000m high - are a trademark of Gran Sabana. Beautiful yet somehow sorrowful, every cliff-face streams with waterfalls, as if the whole mountain is weeping.

For two hours, our plane skimmed between tepuis, passing within 100m of the vertical walls of one of the tallest, El Castillo. Every now and then we glided down to isolated villages, landing bumpily on dirt airstrips to drop off the now half-melted chickens and to pick up passengers, parcels and post.

Arriving at Santa Elena de Uairen in the early afternoon, I was met by my guide, Eric Buschbell, an amiable 34-year-old who runs Backpacker Tours. Working with the London travel firm Journey Latin America, he has organised my five-day tour of Gran Sabana, including all transport, accommodation and meals.

We set off in Eric's four-wheel drive, heading north on the only paved road in a region that covers 35,000 sq km. It isn't what I expected. The rolling grassy hills of Gran Sabana remind me of the Scottish Highlands - but hot and with palm trees. What's more, the roadside scrub features insect-eating plants and dozens of varieties of wild orchids. Hawks and vultures soar overhead.

When we reach the crest of a high hill, we gaze over the escarpment down into the Valley of the Moriche Palms. The dinosaur scenes in Jurassic Park were filmed here. To the left is Monte Roraima, the tepui that inspired Arthur Conan Doyle to write The Lost World.

Further on, we come to Quebrada de Jaspe, where the red jasper rock of the riverbed gives the water an eerily beautiful bloody appearance. It crosses my mind that this is not nature as we know it in the UK. Right on cue a 5ft dark green liophis snake, with bright yellow spine, slithers across my path.

Next stop: Yurani Falls. Although only 5m high, the cascade is 50m wide and packs ferocious power. We climb down the side of the falls, and then crawl and swim behind the water curtain. Reaching a rock ledge near the middle, we sit and gaze out through the golden, sunlit cascades. The gold colour comes from tannin in the water, caused by rotting forest vegetation. Don't be put off. The golden waters are a great natural hair conditioner.

At sunset, we pull over near a precipice, and sit on rocks drinking rum with watermelon juice. This is an ancient Amerindian holy place. All around us are small stone cairns. Across the valley below, dozens of tepuis dot the horizon. These are the oldest mountains in the world, dated at 1,700 million years. In La Gran Sabana, there are nearly 120 tepuis. Half of them have never had anyone on top.

Overnight, we sleep in stone cabins at Kama camp, a Pemon Indian village built next to the 55m Kama Falls. The altitude here is 1,000m, so it gets refreshingly chilly at night.

The following morning, after a breakfast of cheese dumplinas and coffee, we begin the 130km drive to Mantopai. It is dusty, pot-holed dirt roads much of the way. At the village of Kavanayen, a simple lunch is enlivened with kumache - a hot chilli, crunchy termite sauce. An acquired taste.

The next part of our journey takes us off-road across grassland and along a dried river-bed, where the route is sign-posted by arrows painted on rocks. By mid-afternoon, we reach Mantopai camp, on the banks of the Karuai River. Looming behind the stone huts is Sororpan tepui. In silhouette, it looks like the profile of a man's face. After climbing the 80m-high ridge on the opposite bank, we head down into a jungle valley, sighting an ant mound 6m across, jaguar droppings, big blue butterflies, and a deadly bothrops atrax viper sleeping in a branch.

At night, I bathe nude in the river, under the moon and stars. Fireflies glow all around me. Glorious! Until a swarm of puri puri (sandflies) descend and start feasting on my flesh. I get dressed hurriedly and dowse myself in insect repellent. But not before acquiring 30 bites that itch madly for a week.

On day three, I woke at 6am to the unexpected sight of frosty dew on the ground and low clouds completely obscuring the tepuis. For breakfast we down a platter of arepas - thick fried cornbread pancakes - served with eggs and cheese.

Our next destination is the village of Iboribo, where we hire a motorised dug-out canoe to take us down the glass-flat, mirror-surfaced Aponwao river. Above us, Amazon ringed kingfishers dart from tree to tree.

Mooring near the top of the 107m Chinak Meru falls, we trek down a rocky path to the base. The river shoots over the edge in rocket-like plumes of white water. From the rocks below, clouds of mist float upwards and turbulent waves and winds fan outwards. Big yellow butterflies flit in and out of the spray.

Arriving back in Santa Elena de Uairen at dusk, I check into the Hotel Michelle. Basic but clean, with en-suite bathroom and hot water, it is a bargain at US$6 a night. In the evening, I take a wander. This frontier town feels like a Latin version of the Wild West. It is the last Venezuelan settlement before the Brazilian border, and a centre of gold and diamond mining. The many cheap hotels and bars give the place a vaguely sleazy, on-the-edge appeal.

On day four, Eric drives me out to El Pauji, a one-time hippy colony 90 minutes south-west of Santa Elena. From there, we set off on foot to climb El Abismo. It is a gently sloping mountain on the El Pauji side, but has a tepui-like sheer precipice on the other. Ascending through scrub dotted with wild orchids, we sight turkey vultures and iridescent green and violet humming birds. At the summit, from a rock stack on a cliff edge that drops 300m, we have a grandstand view over Brazil.

Further along the mountain, the vegetation changes to light jungle, with lots of moss and lichen. Several two-metre, geometric-shaped spider webs hang suspended from trees and bushes.

After traversing a small rock gorge, we squeeze through a narrow opening into a dark, dank cave 12m high. Hundreds of bats treat us to a chorus of flapping wings and playful squeaks reminiscent of the mischievous critters in the movie Gremlins. The smell of bat droppings is pervasive, but more sickly sweet than putrid.

On the return hike, I feast on wild campanita, a juicy red, bell-shaped flower with a sweet, sharp, citric flavour.

Our final stop is Pozo Esmeralda. A deep green lagoon edged with large boulders, it is fed by a small waterfall and overhung with dense foliage. After a hot day's trekking, the cool water is gorgeously refreshing.

Arriving back in Santa Elena at 7pm, I book into Ya-Koo eco lodge to enjoy a night of affordable luxury. For £25, you get a beautiful stone and timber cabin set in a tropical garden with a rock pool; plus a five-star dinner at night and a magnificent breakfast the next morning. Situated in the forest out of town, Ya-Koo is a nature lover's paradise, with dozens of varieties of exotic birds and butterflies. It was the perfect place to unwind after four exhilarating, adventure-packed days.

Getting there:

Journey Latin America (020-8747 8315, Journey Latin America) offers tailor-made holidays to Venezuela. A 10-night itinerary including the Caribbean beaches of the Paria Peninsula and the Angel Falls, starts at £1,899 per person (based on two sharing) including all flights, hotels with most meals, transfers and excursions. Trip extensions can be arranged for a visit to the Andes, the Llanos, the Orinoco Delta or Los Roques Islands.